The Sfas Emes (5650) says the two mitzvot of Sukkos, the lulav and the sukkah parallel the two names or two different approaches of Yaakov, the approach of Yaakov and of Yisrael. The mitzvah of lulav corresponds to the name Yaakov which is the avodah of fighting against evil forces. The mitzvah of sukkah is the level where the evil forces can't touch. That is why חל שם שמים on the sukkah. The sukkah is above our understanding, it is the point above reason which is connected to the deepest part of our soul. It is interesting that sukkah is deemed above logic when it is also the mitzvah linked to למען ידעו. But it is no contradiction. The understanding of sukkah is beyond our understanding but it is engrained within us. דעת as explained by the Tanya and Nefesh Hachaim means connection. It is the point of connection of the neshama that is not defined by reason but is felt by the person. That is what sukkah represents. It is not that sukkah is beyond sechel, it is deeper. The lulav is the spear we use to combat the forces around us while the sukkah is the point of sitting back and take in our connection to Hashem.
